Qt Quick Application wizards: Qt::AA_EnableHighDpiScaling only on WIN

Setting Qt::AA_EnableHighDpiScaling causes a few graphics backends to
malfunction. This patch reduced the setting of the flag to happen only
on Windows (it is automatically set on macOS with retina).

Task-number: QTBUG-64815
Change-Id: I08fa5d1bd2c93e7a39c23487b684bd3f7b358783
Reviewed-by: Eike Ziller <eike.ziller@qt.io>
Reviewed-by: Laszlo Agocs <laszlo.agocs@qt.io>
Reviewed-by: Sami Nurmenniemi <sami.nurmenniemi@qt.io>

share/qtcreator/templates/wizards/projects/qtquickapplication/main.cpp

@@ -11,7 +11,9 @@ int main(int argc, char *argv[])
     qputenv("QT_IM_MODULE", QByteArray("qtvirtualkeyboard"));
 
 @endif
+#if defined(Q_OS_WIN)
     QCoreApplication::setAttribute(Qt::AA_EnableHighDpiScaling);
+#endif
 
     QGuiApplication app(argc, argv);